The invention relates to a method and apparatus for the pneumatic conveyance of fine material.
A method of the general type to which the invention relates is disclosed in German Auslegeschrift No. 24 61 579. When the aerating or nozzle air is regulated so as to be constant in quantity the pneumatic aerating pressure in the conveyor vessel or the pressure prevailing at the conveyor nozzle corresponds to the filling level of the conveyor vessel (i.e., the column of material resting on the aerating base). As is explained in detail in the German Auslegeschrift, each value of the pneumatic aerating pressure corresponds to a specific discharge capacity of the conveyor vessel. Therefore, if the aerating pressure or the filling level in the conveyor vessel is altered the conveying capacity can be set.
In order to alter the discharge capacity of the conveyor vessel from a minimum value to a maximum value in the known method it is necessary to raise the filling level the conveyor vessel quite considerably. Such an increase in the discharge capacity can only be achieved with a certain delay in response, particularly because of the limited capacity of the feed apparatus (by means of which the material is delivered to the conveyor vessel in order to raise the filling level). The same applies when the discharge capacity of the conveyor vessel is to be reduced from a high value to a low value because the reduction in the conveying capacity of the conveyor vessel depends upon how quickly the filling level in the conveyor vessel and with it the discharge capacity is reduced.
There are cases (for instance the controlled supply of fuel such as coal dust to a burner) in which desired alterations in the discharge capacity of the conveyor vessel must take place particularly quickly.
An object of the invention is to develop further the method referred to so that alterations in the conveying capacity take place particularly quickly, i.e., with a very short delay in response. In addition, the method according to the invention should make it possible to keep the set conveying capacity constant with particular accuracy, even when the material supply to the conveyor vessel takes place by means of a simple on/off switch or fluctuates greatly for other reasons. It also is an object of the invention to provide a conveying method in which apparatus for performing the method can be calibrated particularly accurately and without the aid of a special calibration vessel.